This invention relates to wiring blocks for use primarily in the communications industry. More specifically, this invention relates to an impedance controlled and electrically balanced wiring block assembly.
Communication system and/or network efficiency is directly dependent upon the integrity of the connector scheme employed. Such connector schemes include, for example, standard interfaces for equipment/user access (outlet connector), transmission means (horizontal and backbone cabling), and administration/distribution points (cross-connect and patching facilities). Regardless of the type or capabilities of the transmission media used for an installation, the integrity of the wiring infrastructure is only as good as the performance of the individual components that bind it together.
By way of example, a non-standard connector or pair scheme may require that work area outlets be rewired to accommodate a group move, system change, or an installation with connecting hardware whose installed transmission characteristics are compatible with an existing application but are later found to have inadequate performance when the system is expanded or upgraded to higher transmission rates. Accordingly, connecting hardware without properly qualified design and transmission capabilities, can drain user productivity, compromise system performance and pose a significant barrier to new and emerging applications.
Reliability, connection integrity and durability are also important considerations, since wiring life cycles typically span periods of ten to twenty years. In order to properly address specifications for, and performance of telecommunications connecting hardware, it is preferred to establish a meaningful and accessible point of reference. The primary reference, considered by many to be the international benchmark for commercially based telecommunications components and installations, is standard ANSI/EIA/TIA-568 (TIA-568) Commercial Building Telecommunications Wiring Standard. A supplement Technical Systems Bulletin to TIA-568 is TIA/EIA TSB40 (TSB40), Additional Transmission Specifications for Unshielded Twisted-Pair Connecting Hardware. Among the many aspects of telecommunications cabling covered by these standards are connecting hardware design, reliability and transmission performance. Accordingly, the industry has established a common set of test methods and pass/fail criteria on which performance claims and comparative data may be based.
To determine connecting hardware performance in a data environment, it is preferred to establish test methods and pass/fail criteria that are relevant to a broad range of applications and connector types. Since the relationship between megabits and megahertz depends on the encoding scheme used, performance claims for wiring components that specify bit rates without providing reference to an industry standard or encoding scheme are of little value. Therefore, it is in the interest of both manufacturers and end users to standardize performance information across a wide range of applications. For this reason, application independent standards, such as TIA-568 and TSB40, specify performance criteria in terms of hertz rather than bits per second. This information may then be applied to determine if requirements for specific applications are complied with. For example, many of the performance requirements in the IEEE 802.3i(10BASE-T) standard are specified in megahertz (MHz), and although data is transmitted at 10 Mbps for this application, test "frequencies" are specified in the standard (as high as 15 MHz).
Transmission parameters defined in TSB40 for unshielded twisted pair (UTP) connectors include attenuation and near-end crosstalk (NEXT) and return loss.
Connector attenuation is a measure of the signal power loss through a connector at various frequencies. It is expressed in decibels as a positive, frequency dependent value. The lower the attenuation value, the better the attenuation performance. Since connecting hardware is generally considered to be electrically short relative to the length of cabling between two active devices (i.e., up to 100 meters of cable is typically allowed), the attenuation performance of the connecting hardware is usually not a major performance consideration.
Connector crosstalk is a measure of signal coupling from one pair to another within a connector at various frequencies. Since crosstalk coupling is greatest between transmission segments close to the signal source, near-end crosstalk (as opposed to far-end) is generally considered to be the worst case. Although measured values are negative, near-end crosstalk (NEXT) loss is expressed in decibels as a frequency dependent value. The higher the NEXT loss magnitude, the better the crosstalk performance.
Connector return loss is a measure of the degree of impedance matching between the cable and connector. When impedance discontinues exist, signal reflections result. These reflections may be measured and expressed in terms of return loss. This parameter is also expressed in decibels as a frequency dependent value. The higher the return loss magnitude, the better the return loss performance.
Since most high speed transmission applications that are designed for use with twisted-pair cabling do not operate in a full duplex mode (i.e., transmit and receive signals are not carried over the same pair), the effects of signal reflections, as caused by connectors, are generally not significant with respect to the ability of the twisted pair cabling to support existing applications that are designed for use with twisted pair cabling. However, for future high speed applications that may employ full duplex transmission, connector return loss poses a significant limitation unless properly controlled.
The net effect of these parameters on channel performance may be expressed in signal-to-noise ratio (SNR). For connecting hardware, the parameter that has been found to have the greatest impact on SNR is near-end crosstalk.
Several industry standards specify multiple performance levels of UTP cabling components have been established. For example, Category 3, 4 and 5 cable and connecting hardware are specified in EIA/TIA TSB-36 & TIA/EIA TSB40 respectively. In these specifications, transmission requirements for Category 3 components are specified up to 16 MHz. They will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 10 Mbps, such as 4 MBps Token Ring and 10BASE-T.
Transmission requirements for Category 4 components are specified up to 20 MHz. They will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 16 Mbps, such as Token Ring.
Transmission requirements for Category 5 components are specified up to 100 MHz. They are expected to support UTP voice as well as emerging video and ANSI X3T9 series data applications with transmission rates up to 100 Mbps, such as 100 Mbps Twisted-Pair Physical Media Dependent (TP-PMD) and 155 Mbps asynchronous transfer for mode (ATM) applications.
In order for a UTP connector to be qualified for a given performance category, it must meet all applicable transmission requirements regardless of design or intended use. The challenge of meeting transmission criteria is compounded by the fact that connector categories apply to worst case performance. For example, a work area outlet that meets Category 5 NEXT requirements for all combinations of pairs except one, which meets Category 3, may only be classified as a Category 3 connector (provided that it meets all other applicable requirements).
Wiring/connector blocks with circuit interrupt capability, sometimes referred to as "break-test" capability, are well known. For example, such products are described in U.S. Pat. Nos. 5,044,979; 4,547,034 and 4,615,576. These patents describe wiring/connector blocks having two rows of wire termination connectors that are separated by an optional connector for providing interruptable electrical connections between the two rows of wire termination connectors. An important limitation of these prior art blocks is that the spatial alignment of the adjacent contacts allows crosstalk coupling to occur within the connector between the input and output terminations.
The regular clip spacing causes uniform capacitative coupling between adjacent rows of clips such that, when used with twisted-pair wires, the "tip" and "ring" wires that constitute a pair (balanced transmission line) is equal to that of adjacent conductors from different pairs. Since the crosstalk performance is determined by the degree of capacitive imbalance between pairs (i. e., the difference in capacitive coupling between each conductor of a pair and a conductor of another pair), the constant spacing between rows poses a limitation in terms of crosstalk performance between adjacent circuits. The extent of this limitation is manifested in terms of transmission performance. Transmission tests of these products show that they do not satisfy Category 5 requirements. Therefore, their ability to support high speed signaling applications is limited to those supported by cabling systems of Category 4 or less.
AT&T Technologies 110T-series terminal block employs two rows of known 100C series connecting blocks with its bottom insulation displacement terminals connected to bent tail leads that extend from contacts positioned between the two rows of 110C connectors. These contacts are positioned and housed to provide a circuit interrupt capability. As with the devices described in U.S. Pat. Nos. 5,044,979; 4,547,034 and 4,615,576, the regular contact spacing and significant electrical length of this product have the effect of limiting transmission performance, and hence its ability to support advanced networking applications. In this case, transmission performance is limited to Category 4.
U.S. Pat. No. 5,160,273 discloses a "break-test" device which employs positioned shielding to improve crosstalk isolation between pairs. Although this design provides a benefit in terms of improved crosstalk performance over the above discussed prior art devices, it is bereft with other limitations such as the by additional expense of the shield element and numerous additional secondary operations required to assemble the finished product. The shield also raises the risk of compromising electrical isolation between signal carriers.
Prior art methods also exist for achieving electrical balance between pairs to improve crosstalk performance of other types of connectors used with balancing cabling. In particular, U.S. patent application Ser. No. 07/993,480 filed Dec. 18, 1992 discloses an electrically balanced connector assembly for modular jack outlet connectors. However, modular jack outlet connectors do not require internal "break-test" capability. Heretofore wiring blocks have not offered compensation means to achieve electrical balance between pairs.